use anyhow::{Context, Result};
use calamine::{open_workbook, Data, DataType, Reader, Xlsx};
use chrono::{Duration, NaiveDate};
use serde::{Deserialize, Serialize};
use std::path::Path;

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct Student {
    pub id: Option<String>,
    pub year: Option<String>,
    pub grade: Option<String>,
    pub class: Option<String>,
    pub name: String,
}

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct AttendanceRecord {
    pub student: Student,
    // Date, Teacher Name, and attendance count (1.0 for present)
    pub attendance: Vec<(NaiveDate, Option<String>, f64)>,
}

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct ClassData {
    pub class_name: String,
    pub records: Vec<AttendanceRecord>,
}

pub fn read_attendance_file<P: AsRef<Path>>(path: P) -> Result<Vec<ClassData>> {
    let mut workbook: Xlsx<_> = open_workbook(path).context("Failed to open Excel file")?;
    let mut classes = Vec::new();

    for sheet_name in workbook.sheet_names().to_owned() {
        if let Ok(range) = workbook.worksheet_range(&sheet_name) {
            let mut records = Vec::new();
            let mut dates = Vec::new();
            let mut date_col_indices = Vec::new();

            // Find header row (row 2, index 1)
            if range.height() < 2 {
                continue;
            }

            // Parse headers to find date columns
            // Assuming row 2 (index 1) contains headers and dates
            let header_row = range.rows().nth(1).unwrap();
            
            for (col_idx, cell) in header_row.iter().enumerate() {
                // Dates in Excel are often floats or ints (serial dates)
                // Check if the cell value looks like a date (e.g., > 40000)
                if let Some(float_val) = cell.as_f64() {
                    if float_val > 40000.0 && float_val < 50000.0 {
                        // Convert serial date to NaiveDate
                        // Excel base date is usually 1899-12-30
                        let base_date = NaiveDate::from_ymd_opt(1899, 12, 30).unwrap();
                        let days = float_val as i64;
                        if let Some(date) = base_date.checked_add_signed(Duration::days(days)) {
                            dates.push(date);
                            date_col_indices.push(col_idx);
                        }
                    }
                }
            }

            if dates.is_empty() {
                // Skip sheets without dates
                continue;
            }

            // Find Teacher Row
            // Scan all rows to find "授课教师确认签名"
            let mut teacher_names = vec![None; dates.len()];
            for row in range.rows() {
                if let Some(first_cell) = row.first() {
                    if let Data::String(s) = first_cell {
                        if s.contains("授课教师确认签名") {
                            // Found teacher row
                            for (i, &col_idx) in date_col_indices.iter().enumerate() {
                                if col_idx < row.len() {
                                    if let Data::String(name) = &row[col_idx] {
                                        let trimmed = name.trim();
                                        if !trimmed.is_empty() {
                                            teacher_names[i] = Some(trimmed.to_string());
                                        }
                                    }
                                }
                            }
                            break;
                        }
                    }
                }
            }

            // Iterate over data rows (starting from row 4, index 3)
            // Row 1: Title, Row 2: Headers, Row 3: Weekdays, Row 4: Data
            for row in range.rows().skip(3) {
                // Check if row has a name (Column E, index 4)
                // If name is empty, skip
                let name_cell = &row[4];
                let name = match name_cell {
                    Data::String(s) => s.trim().to_string(),
                    _ => continue, // Skip if no name
                };

                if name.is_empty() || name == "姓名" || name == "到班人数" || name.contains("授课教师") {
                    continue;
                }

                let id = row[0].to_string();
                let year = row[1].to_string();
                let grade = row[2].to_string();
                let class_info = row[3].to_string();

                let student = Student {
                    id: if id.is_empty() { None } else { Some(id) },
                    year: if year.is_empty() { None } else { Some(year) },
                    grade: if grade.is_empty() { None } else { Some(grade) },
                    class: if class_info.is_empty() { None } else { Some(class_info) },
                    name,
                };

                let mut attendance_entries = Vec::new();

                for (i, &col_idx) in date_col_indices.iter().enumerate() {
                    if col_idx < row.len() {
                        let cell = &row[col_idx];
                        // Check for "1" or numeric 1
                        let is_present = match cell {
                            Data::Int(v) => *v == 1,
                            Data::Float(v) => (*v - 1.0).abs() < 1e-6,
                            Data::String(s) => s.trim() == "1",
                            _ => false,
                        };

                        if is_present {
                            if i < dates.len() {
                                attendance_entries.push((dates[i], teacher_names[i].clone(), 1.0));
                            }
                        }
                    }
                }

                if !attendance_entries.is_empty() {
                    records.push(AttendanceRecord {
                        student,
                        attendance: attendance_entries,
                    });
                }
            }

            if !records.is_empty() {
                classes.push(ClassData {
                    class_name: sheet_name.clone(),
                    records,
                });
            }
        }
    }

    Ok(classes)
}