use aamos_core::{Currency, DecisionSource, LedgerError, LedgerResult, Money, Period, TenantId};
use aamos_ledger::{EntryStatus, JournalEntry, JournalLine, SourceType};
use chrono::{Datelike, NaiveDate};
use std::io::{BufRead, BufReader, Read};
use uuid::Uuid;

/// Parse SIE4 format into JournalEntry structs.
///
/// SIE4 is a Swedish accounting data exchange format. Each record starts with
/// a `#TAG` followed by fields enclosed in curly braces `{}`.
///
/// Relevant tags for import:
/// - #FLAGGA — file flag (0 = normal)
/// - #FORMAT — encoding (PC8/PC850/UTF8)
/// - #SIETYP — SIE type (4 = SIE4)
/// - #FNR — company number
/// - #FNAMN — company name
/// - #ORGNR — organization number
/// - #KPTYP — chart of accounts type (BAS96, BAS97, EUBAS97)
/// - #RAR — fiscal year (0 = current, -1 = previous, etc.)
/// - #KONTO — account definition (#KONTO {account_number} {account_name})
/// - #VER — voucher/verifikation (#VER {series} {entry_number} {date} {description} {registration_date} {registered_by})
/// - #TRANS — transaction line within a #VER block (#TRANS {account} {amount} {date} {description} {quantity})
/// - #PBUDGET — periodic budget
/// - #PSALDO — periodic balance
/// - #SRU — SRU code mapping
/// - #DIM — dimension definition
/// - #UNDERDIM — sub-dimension
/// - #OBJ — object within dimension
pub fn parse_entries<R: Read>(reader: R) -> LedgerResult<Vec<JournalEntry>> {
    let buf_reader = BufReader::new(reader);
    let mut lines = Vec::new();
    let mut current_ver: Option<VerBuilder> = None;
    let mut entries: Vec<JournalEntry> = Vec::new();
    let mut line_no = 0usize;

    for raw_line in buf_reader.lines() {
        line_no += 1;
        let raw_line = raw_line.map_err(|e| {
            LedgerError::BadRequest(format!("SIE4 read error at line {}: {}", line_no, e))
        })?;

        let line = raw_line.trim();
        if line.is_empty() || line.starts_with("//") {
            continue;
        }

        // Normalize: SIE4 uses CP437 or UTF-8; we assume UTF-8 here.
        lines.push(line.to_string());

        if line.starts_with("#VER ") {
            // Flush previous #VER if any
            if let Some(ver) = current_ver.take() {
                entries.push(ver.build()?);
            }
            current_ver = Some(parse_ver_line(line, line_no)?);
        } else if line.starts_with("#TRANS ") {
            let ver = current_ver
                .as_mut()
                .ok_or_else(|| LedgerError::Validation(format!(
                    "SIE4: #TRANS without #VER at line {}",
                    line_no
                )))?;
            ver.trans.push(parse_trans_line(line, line_no)?);
        } else if line.starts_with("#RTRANS ") {
            // RTRANS = reversed transaction (handled same as TRANS with negated amount)
            let ver = current_ver
                .as_mut()
                .ok_or_else(|| LedgerError::Validation(format!(
                    "SIE4: #RTRANS without #VER at line {}",
                    line_no
                )))?;
            ver.trans.push(parse_rtrans_line(line, line_no)?);
        } else if line.starts_with("#BTRANS ") {
            // BTRANS = budget transaction (skip for journal import)
            // Budget transactions are not part of the actual journal.
        } else if line == "}" {
            // End of #VER block (optional in some SIE4 files)
            if let Some(ver) = current_ver.take() {
                entries.push(ver.build()?);
            }
        }
        // Other tags are ignored for journal-entry import
    }

    // Flush final #VER
    if let Some(ver) = current_ver.take() {
        entries.push(ver.build()?);
    }

    Ok(entries)
}

// ── Internal builders ─────────────────────────────────────────────────────

struct VerBuilder {
    series: String,
    entry_number: String,
    date: NaiveDate,
    description: String,
    _reg_date: Option<NaiveDate>,
    reg_by: Option<String>,
    trans: Vec<TransLine>,
}

struct TransLine {
    account: String,
    amount: f64, // in SEK, positive = debit, negative = credit
    _date: Option<NaiveDate>,
    description: Option<String>,
    _quantity: Option<f64>,
    cost_center: Option<String>,
    project: Option<String>,
}

impl VerBuilder {
    fn build(self) -> LedgerResult<JournalEntry> {
        let entry_number = self.entry_number.parse::<i64>().ok();

        let fiscal_year = self.date.year();
        let month = self.date.month() as u8;
        let period = Period::new(fiscal_year, month)?;

        let trace_id = Uuid::new_v4();
        let correlation_id = Uuid::new_v4();

        let mut lines: Vec<JournalLine> = Vec::with_capacity(self.trans.len());
        for (idx, t) in self.trans.iter().enumerate() {
            let (debit, credit) = if t.amount >= 0.0 {
                (Some(Money::from_decimal(t.amount)), None)
            } else {
                (None, Some(Money::from_decimal(-t.amount)))
            };

            lines.push(JournalLine {
                id: Uuid::new_v4(),
                entry_id: Uuid::nil(), // filled later by storage layer
                tenant_id: TenantId::new("imported"),
                line_number: (idx + 1) as i32,
                account_number: t.account.clone(),
                account_name: None,
                debit,
                credit,
                currency: Currency::SEK,
                amount_base: None,
                vat_code: None,
                vat_amount: None,
                cost_center: t.cost_center.clone(),
                project_code: t.project.clone(),
                description: t.description.clone(),
                metadata: serde_json::Value::Object(serde_json::Map::new()),
            });
        }

        Ok(JournalEntry {
            id: Uuid::new_v4(),
            tenant_id: TenantId::new("imported"),
            entry_number,
            fiscal_year,
            period,
            entry_date: self.date,
            description: self.description,
            reference: Some(format!("{}-{}", self.series, self.entry_number)),
            source_type: SourceType::ImportSie,
            source_id: None,
            status: EntryStatus::Draft,
            void_reason: None,
            voided_at: None,
            voided_by: None,
            trace_id,
            correlation_id,
            user_id: self.reg_by.unwrap_or_else(|| "sie-import".to_string()),
            decision_source: DecisionSource::System,
            metadata: serde_json::Value::Object(serde_json::Map::new()),
            created_at: chrono::Utc::now(),
            posted_at: None,
            lines,
        })
    }
}

// ── Line parsers ──────────────────────────────────────────────────────────

/// Parse a #VER line.
///
/// Format: #VER {series} {entry_number} {date} {description} {registration_date} {registered_by}
///
/// Example: #VER A 1 20260115 "Faktura #1234" 20260115 "admin"
fn parse_ver_line(line: &str, line_no: usize) -> LedgerResult<VerBuilder> {
    let content = line.strip_prefix("#VER ").unwrap_or("").trim();
    let tokens = tokenize_sie_line(content);

    if tokens.len() < 4 {
        return Err(LedgerError::Validation(format!(
            "SIE4: #VER too few fields at line {}: expected at least 4, got {}",
            line_no,
            tokens.len()
        )));
    }

    let series = unquote(&tokens[0]);
    let entry_number = unquote(&tokens[1]);
    let date = parse_sie_date(&tokens[2], line_no)?;
    let description = unquote(&tokens[3]);

    let _reg_date = tokens.get(4).and_then(|d| parse_sie_date(d, line_no).ok());
    let reg_by = tokens.get(5).map(|s| unquote(s));

    Ok(VerBuilder {
        series,
        entry_number,
        date,
        description,
        _reg_date,
        reg_by,
        trans: Vec::new(),
    })
}

/// Parse a #TRANS line.
///
/// Format: #TRANS {account} {amount} {date} {description} {quantity} {sign} {dimension/object...}
///
/// Example: #TRANS 1510 {1250.50} 20260115 "Kundfordran"
///
/// Amount is enclosed in {} and may be negative (credit).
fn parse_trans_line(line: &str, line_no: usize) -> LedgerResult<TransLine> {
    let content = line.strip_prefix("#TRANS ").unwrap_or("").trim();
    let tokens = tokenize_sie_line(content);

    if tokens.len() < 2 {
        return Err(LedgerError::Validation(format!(
            "SIE4: #TRANS too few fields at line {}: expected at least 2, got {}",
            line_no,
            tokens.len()
        )));
    }

    let account = unquote(&tokens[0]);
    let amount = parse_sie_amount(&tokens[1], line_no)?;
    let date = tokens.get(2).and_then(|d| parse_sie_date(d, line_no).ok());
    let description = tokens.get(3).map(|s| unquote(s));
    let quantity = tokens.get(4).and_then(|q| parse_sie_amount(q, line_no).ok());

    // Parse dimension/object pairs if present (e.g. "1" "{cc}" "6" "{proj}")
    let mut cost_center = None;
    let mut project = None;
    let mut i = 6usize;
    while i + 1 < tokens.len() {
        let dim = unquote(&tokens[i]);
        let obj = unquote(&tokens[i + 1]);
        match dim.as_str() {
            "1" => cost_center = Some(obj),
            "6" => project = Some(obj),
            _ => {}
        }
        i += 2;
    }

    Ok(TransLine {
        account,
        amount,
        _date: date,
        description,
        _quantity: quantity,
        cost_center,
        project,
    })
}

/// Parse a #RTRANS line (reversed transaction).
/// Same as #TRANS but amount is negated.
fn parse_rtrans_line(line: &str, line_no: usize) -> LedgerResult<TransLine> {
    let mut trans = parse_trans_line(line.replacen("#RTRANS ", "#TRANS ", 1).as_str(), line_no)?;
    trans.amount = -trans.amount;
    Ok(trans)
}

// ── Tokenizer ─────────────────────────────────────────────────────────────

/// Tokenize a SIE4 line respecting quoted strings and braced amounts.
///
/// SIE4 fields are separated by spaces, but:
/// - Quoted strings `"..."` are treated as single tokens (quotes removed by unquote)
/// - Braced amounts `{...}` are treated as single tokens
/// - Bare tokens are passed through
fn tokenize_sie_line(line: &str) -> Vec<String> {
    let mut tokens = Vec::new();
    let mut chars = line.chars().peekable();
    let mut current = String::new();
    let mut in_quotes = false;
    let mut in_braces = false;

    while let Some(ch) = chars.next() {
        if in_quotes {
            if ch == '"' {
                in_quotes = false;
                tokens.push(current.clone());
                current.clear();
            } else {
                current.push(ch);
            }
        } else if in_braces {
            if ch == '}' {
                in_braces = false;
                tokens.push(current.clone());
                current.clear();
            } else {
                current.push(ch);
            }
        } else {
            match ch {
                '"' => {
                    if !current.is_empty() {
                        tokens.push(current.clone());
                        current.clear();
                    }
                    in_quotes = true;
                }
                '{' => {
                    if !current.is_empty() {
                        tokens.push(current.clone());
                        current.clear();
                    }
                    in_braces = true;
                }
                ' ' | '\t' => {
                    if !current.is_empty() {
                        tokens.push(current.clone());
                        current.clear();
                    }
                }
                _ => current.push(ch),
            }
        }
    }

    if !current.is_empty() {
        tokens.push(current);
    }

    tokens
}

// ── Helpers ───────────────────────────────────────────────────────────────

fn unquote(s: &str) -> String {
    s.trim_matches('"').to_string()
}

/// Parse SIE4 date: YYYYMMDD
fn parse_sie_date(s: &str, line_no: usize) -> LedgerResult<NaiveDate> {
    let s = unquote(s);
    if s.len() != 8 {
        return Err(LedgerError::Validation(format!(
            "SIE4: invalid date '{}' at line {}, expected YYYYMMDD",
            s, line_no
        )));
    }
    let year = s[0..4].parse::<i32>().map_err(|_| {
        LedgerError::Validation(format!("SIE4: invalid year in date '{}' at line {}", s, line_no))
    })?;
    let month = s[4..6].parse::<u32>().map_err(|_| {
        LedgerError::Validation(format!("SIE4: invalid month in date '{}' at line {}", s, line_no))
    })?;
    let day = s[6..8].parse::<u32>().map_err(|_| {
        LedgerError::Validation(format!("SIE4: invalid day in date '{}' at line {}", s, line_no))
    })?;
    NaiveDate::from_ymd_opt(year, month, day).ok_or_else(|| {
        LedgerError::Validation(format!(
            "SIE4: invalid date '{}' at line {}",
            s, line_no
        ))
    })
}

/// Parse SIE4 amount. Amounts may be in braces or bare.
fn parse_sie_amount(s: &str, line_no: usize) -> LedgerResult<f64> {
    let s = unquote(s).trim_matches('{').trim_matches('}').replace(',', ".");
    s.parse::<f64>().map_err(|_| {
        LedgerError::Validation(format!(
            "SIE4: invalid amount '{}' at line {}",
            s, line_no
        ))
    })
}

// ── Tests ─────────────────────────────────────────────────────────────────

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_tokenize_simple() {
        let tokens = tokenize_sie_line(r#"A 1 20260115 "Faktura #1234""#);
        assert_eq!(tokens, vec!["A", "1", "20260115", "Faktura #1234"]);
    }

    #[test]
    fn test_tokenize_braced_amount() {
        let tokens = tokenize_sie_line(r#"1510 {1250.50} 20260115 "Kundfordran""#);
        assert_eq!(tokens, vec!["1510", "1250.50", "20260115", "Kundfordran"]);
    }

    #[test]
    fn test_tokenize_negative_amount() {
        let tokens = tokenize_sie_line(r#"3001 {-1000.00} 20260115 "Intäkt""#);
        assert_eq!(tokens, vec!["3001", "-1000.00", "20260115", "Intäkt"]);
    }

    #[test]
    fn test_parse_sie_date() {
        let d = parse_sie_date("20260115", 1).unwrap();
        assert_eq!(d, NaiveDate::from_ymd_opt(2026, 1, 15).unwrap());
    }

    #[test]
    fn test_parse_sie_amount() {
        let a = parse_sie_amount("{1250.50}", 1).unwrap();
        assert!((a - 1250.50).abs() < 0.001);
    }

    #[test]
    fn test_parse_sie_amount_negative() {
        let a = parse_sie_amount("{-1000.00}", 1).unwrap();
        assert!((a - (-1000.0)).abs() < 0.001);
    }

    #[test]
    fn test_parse_ver_line() {
        let ver = parse_ver_line(r#"#VER A 1 20260115 "Faktura #1234" 20260115 "admin""#, 1).unwrap();
        assert_eq!(ver.series, "A");
        assert_eq!(ver.entry_number, "1");
        assert_eq!(ver.date, NaiveDate::from_ymd_opt(2026, 1, 15).unwrap());
        assert_eq!(ver.description, "Faktura #1234");
        assert_eq!(ver.reg_by, Some("admin".to_string()));
    }

    #[test]
    fn test_parse_trans_line_debit() {
        let trans = parse_trans_line(r#"#TRANS 1510 {1250.50} 20260115 "Kundfordran""#, 1).unwrap();
        assert_eq!(trans.account, "1510");
        assert!((trans.amount - 1250.50).abs() < 0.001);
        assert_eq!(trans._date, Some(NaiveDate::from_ymd_opt(2026, 1, 15).unwrap()));
        assert_eq!(trans.description, Some("Kundfordran".to_string()));
    }

    #[test]
    fn test_parse_trans_line_credit() {
        let trans = parse_trans_line(r#"#TRANS 3001 {-1000.00} 20260115 "Intäkt""#, 1).unwrap();
        assert_eq!(trans.account, "3001");
        assert!((trans.amount - (-1000.0)).abs() < 0.001);
    }

    #[test]
    fn test_parse_rtrans_line() {
        let trans = parse_rtrans_line(r#"#RTRANS 3001 {1000.00} 20260115 "Korrigering""#, 1).unwrap();
        assert_eq!(trans.account, "3001");
        assert!((trans.amount - (-1000.0)).abs() < 0.001);
    }

    #[test]
    fn test_parse_full_sie4() {
        let sie4_data = r#"#FLAGGA 0
#FORMAT PC8
#SIETYP 4
#FNR 1
#FNAMN "Testföretag AB"
#ORGNR 5566778899
#KPTYP BAS2024
#VER A 1 20260115 "Faktura #1234"
{
#TRANS 1510 {125000.00} 20260115 "Kundfordran"
#TRANS 3001 {-100000.00} 20260115 "Konsultintäkter"
#TRANS 2611 {-25000.00} 20260115 "Utgående moms 25%"
}
"#;

        let entries = parse_entries(sie4_data.as_bytes()).unwrap();
        assert_eq!(entries.len(), 1);

        let entry = &entries[0];
        assert_eq!(entry.fiscal_year, 2026);
        assert_eq!(entry.period.to_string(), "2026-01");
        assert_eq!(entry.entry_date, NaiveDate::from_ymd_opt(2026, 1, 15).unwrap());
        assert_eq!(entry.description, "Faktura #1234");
        assert_eq!(entry.lines.len(), 3);
        assert!(entry.is_balanced());

        // Line 1: debit 125000
        assert_eq!(entry.lines[0].account_number, "1510");
        assert_eq!(entry.lines[0].debit, Some(Money(12500000)));
        assert_eq!(entry.lines[0].credit, None);

        // Line 2: credit 100000
        assert_eq!(entry.lines[1].account_number, "3001");
        assert_eq!(entry.lines[1].debit, None);
        assert_eq!(entry.lines[1].credit, Some(Money(10000000)));

        // Line 3: credit 25000
        assert_eq!(entry.lines[2].account_number, "2611");
        assert_eq!(entry.lines[2].debit, None);
        assert_eq!(entry.lines[2].credit, Some(Money(2500000)));
    }

    #[test]
    fn test_parse_multiple_ver() {
        let sie4_data = r#"#VER A 1 20260115 "Faktura 1"
#TRANS 1510 {10000.00}
#TRANS 3001 {-10000.00}
#VER A 2 20260116 "Faktura 2"
#TRANS 1510 {20000.00}
#TRANS 3001 {-20000.00}
"#;

        let entries = parse_entries(sie4_data.as_bytes()).unwrap();
        assert_eq!(entries.len(), 2);
        assert_eq!(entries[0].description, "Faktura 1");
        assert_eq!(entries[1].description, "Faktura 2");
    }

    #[test]
    fn test_parse_with_cost_center_and_project() {
        let sie4_data = r#"#VER A 1 20260115 "Kostnad"
#TRANS 6991 {5000.00} 20260115 "Resa" {} {} "1" "CC01" "6" "PROJ01"
"#;

        let entries = parse_entries(sie4_data.as_bytes()).unwrap();
        assert_eq!(entries.len(), 1);
        let line = &entries[0].lines[0];
        assert_eq!(line.cost_center, Some("CC01".to_string()));
        assert_eq!(line.project_code, Some("PROJ01".to_string()));
    }

    #[test]
    fn test_empty_sie4() {
        let entries = parse_entries("#FLAGGA 0\n".as_bytes()).unwrap();
        assert!(entries.is_empty());
    }

    #[test]
    fn test_unbalanced_entry_still_parsed() {
        // Parser does not enforce balance; that is a validation concern
        let sie4_data = r#"#VER A 1 20260115 "Obalanserad"
#TRANS 1510 {10000.00}
#TRANS 3001 {-5000.00}
"#;

        let entries = parse_entries(sie4_data.as_bytes()).unwrap();
        assert_eq!(entries.len(), 1);
        assert!(!entries[0].is_balanced());
    }
}