from odoo import api, fields, models
from odoo.exceptions import ValidationError


class McMark(models.Model):
    _name = "mc.mark"
    _description = "Mark"
    _order = "exam_id, student_id"
    _rec_name = "display_name"

    exam_id = fields.Many2one("mc.exam", string="Exam", required=True, ondelete="cascade")
    student_id = fields.Many2one("mc.student", string="Student", required=True, ondelete="restrict")
    marks_obtained = fields.Float(string="Marks Obtained", required=True)
    grade = fields.Char(string="Grade", compute="_compute_grade", store=True)

    _exam_student_uniq = models.Constraint(
        "unique(exam_id, student_id)",
        "This student already has marks recorded for this exam.",
    )

    @api.depends("student_id.name", "exam_id.display_name")
    def _compute_display_name(self):
        for mark in self:
            mark.display_name = "%s - %s" % (mark.student_id.name or "?", mark.exam_id.display_name or "?")

    @api.depends("marks_obtained", "exam_id.max_marks", "exam_id.batch_id.program_id.grading_scale_id.interval_ids.threshold")
    def _compute_grade(self):
        for mark in self:
            scale = mark.exam_id.batch_id.program_id.grading_scale_id
            if not scale or not mark.exam_id.max_marks:
                mark.grade = False
                continue
            percentage = mark.marks_obtained / mark.exam_id.max_marks * 100
            interval = scale.get_grade_interval(percentage)
            mark.grade = interval.letter if interval else False

    @api.constrains("marks_obtained", "exam_id")
    def _check_marks_within_range(self):
        for mark in self:
            if mark.marks_obtained < 0 or mark.marks_obtained > mark.exam_id.max_marks:
                raise ValidationError(
                    "Marks obtained (%.2f) must be between 0 and the exam's max marks (%.2f)." % (
                        mark.marks_obtained, mark.exam_id.max_marks,
                    )
                )