/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/. */

//! Specified types for CSS Easing functions.
use crate::parser::{Parse, ParserContext};
use crate::piecewise_linear::{PiecewiseLinearFunction, PiecewiseLinearFunctionBuilder};
use crate::values::computed::easing::TimingFunction as ComputedTimingFunction;
use crate::values::computed::{Context, ToComputedValue};
use crate::values::generics::easing::TimingFunction as GenericTimingFunction;
use crate::values::generics::easing::{StepPosition, TimingKeyword};
use crate::values::specified::percentage::ToPercentage;
use crate::values::specified::{AnimationName, Integer, Number, Percentage};
use cssparser::{match_ignore_ascii_case, Delimiter, Parser, Token};
use selectors::parser::SelectorParseErrorKind;
use style_traits::{ParseError, StyleParseErrorKind};

/// A specified timing function.
pub type TimingFunction = GenericTimingFunction<Integer, Number, PiecewiseLinearFunction>;

impl Parse for TimingFunction {
    fn parse(context: &ParserContext, input: &mut Parser) -> Result<Self, ParseError> {
        if let Ok(keyword) = input.try_parse(TimingKeyword::parse) {
            return Ok(GenericTimingFunction::Keyword(keyword));
        }
        if let Ok(ident) = input.try_parse(|i| i.expect_ident_cloned()) {
            let position = match_ignore_ascii_case! { &ident,
                "step-start" => StepPosition::Start,
                "step-end" => StepPosition::End,
                _ => {
                    return Err(ParseError::custom(
                        SelectorParseErrorKind::UnexpectedIdent
                    ));
                },
            };
            return Ok(GenericTimingFunction::Steps(Integer::new(1), position));
        }
        let function = input.expect_function()?.clone();
        input.parse_nested_block(move |i| {
            match_ignore_ascii_case! { &function,
                "cubic-bezier" => Self::parse_cubic_bezier(context, i),
                "steps" => Self::parse_steps(context, i),
                "linear" => Self::parse_linear_function(context, i),
                _ => Err(ParseError::custom(StyleParseErrorKind::UnexpectedFunction)),
            }
        })
    }
}

impl TimingFunction {
    fn parse_cubic_bezier(context: &ParserContext, input: &mut Parser) -> Result<Self, ParseError> {
        let x1 = Number::parse(context, input)?;
        input.expect_comma()?;
        let y1 = Number::parse(context, input)?;
        input.expect_comma()?;
        let x2 = Number::parse(context, input)?;
        input.expect_comma()?;
        let y2 = Number::parse(context, input)?;

        // TODO(Bug 2037743) - Enable calc()-expressions that can only be resolved at
        // computed value time (due to relative lengths, sibling-index(), etc.).
        if let (Some(x1), Some(_), Some(x2), Some(_)) =
            (x1.resolve(), y1.resolve(), x2.resolve(), y2.resolve())
        {
            if !(0.0..=1.0).contains(&x1) || !(0.0..=1.0).contains(&x2) {
                return Err(ParseError::custom(StyleParseErrorKind::UnspecifiedError));
            }
        } else {
            return Err(ParseError::custom(StyleParseErrorKind::UnspecifiedError));
        }

        Ok(GenericTimingFunction::CubicBezier { x1, y1, x2, y2 })
    }

    fn parse_steps(context: &ParserContext, input: &mut Parser) -> Result<Self, ParseError> {
        let steps = Integer::parse_positive(context, input)?;
        let position = input
            .try_parse(|i| {
                i.expect_comma()?;
                StepPosition::parse(i)
            })
            .unwrap_or(StepPosition::End);

        // TODO(Bug 2037743) - Enable calc()-expressions that can only be resolved at
        // computed value time (due to relative lengths, sibling-index(), etc.).
        let num_steps = match steps.resolve() {
            Some(v) => v,
            None => return Err(ParseError::custom(StyleParseErrorKind::UnspecifiedError)),
        };

        // jump-none accepts a positive integer greater than 1.
        // FIXME(emilio): The spec asks us to avoid rejecting it at parse
        // time except until computed value time.
        //
        // It's not totally clear it's worth it though, and no other browser
        // does this.
        if position == StepPosition::JumpNone && num_steps <= 1 {
            return Err(ParseError::custom(StyleParseErrorKind::UnspecifiedError));
        }
        Ok(GenericTimingFunction::Steps(steps, position))
    }

    fn parse_linear_function(
        context: &ParserContext,
        input: &mut Parser,
    ) -> Result<Self, ParseError> {
        let mut builder = PiecewiseLinearFunctionBuilder::default();
        let mut num_specified_stops = 0;
        // Closely follows `parse_comma_separated`, but can generate multiple entries for one comma-separated entry.
        loop {
            input.parse_until_before(Delimiter::Comma, |i| {
                let builder = &mut builder;
                let mut input_start = i.try_parse(|i| Percentage::parse(context, i)).ok();
                let mut input_end = i.try_parse(|i| Percentage::parse(context, i)).ok();

                let output = Number::parse(context, i)?;
                if input_start.is_none() {
                    debug_assert!(input_end.is_none(), "Input end parsed without input start?");
                    input_start = i.try_parse(|i| Percentage::parse(context, i)).ok();
                    input_end = i.try_parse(|i| Percentage::parse(context, i)).ok();
                }

                // TODO(Bug 2037743) - Enable calc()-expressions that can only be resolved at
                // computed value time (due to relative lengths, sibling-index(), etc.).
                let output = match output.resolve() {
                    Some(v) => v,
                    None => return Err(ParseError::custom(StyleParseErrorKind::UnspecifiedError)),
                };
                if matches!(input_start.as_ref().or(input_end.as_ref()), Some(p) if p.resolve().is_none()) {
                    return Err(ParseError::custom(StyleParseErrorKind::UnspecifiedError));
                }

                let has_input_start = input_start.is_some();
                builder.push(
                    output,
                    input_start.map(|v| v.to_percentage().unwrap()),
                );
                num_specified_stops += 1;
                if input_end.is_some() {
                    debug_assert!(has_input_start, "Input end valid but not input start?");
                    builder.push(output, input_end.map(|v| v.to_percentage().unwrap()));
                }

                Ok(())
            })?;

            match input.next() {
                Err(_) => break,
                Ok(&Token::Comma) => continue,
                Ok(_) => unreachable!(),
            }
        }
        // By spec, specifying only a single stop makes the function invalid, even if that single entry may generate
        // two entries.
        if num_specified_stops < 2 {
            return Err(ParseError::custom(StyleParseErrorKind::UnspecifiedError));
        }

        Ok(GenericTimingFunction::LinearFunction(builder.build()))
    }

    /// Returns true if the name matches any keyword.
    #[inline]
    pub fn match_keywords(name: &AnimationName) -> bool {
        if let Some(name) = name.as_atom() {
            #[cfg(feature = "gecko")]
            return name.with_str(|n| TimingKeyword::from_ident(n).is_ok());
            #[cfg(feature = "servo")]
            return TimingKeyword::from_ident(name).is_ok();
        }
        false
    }
}

// We need this for converting the specified TimingFunction into computed TimingFunction without
// Context (for some FFIs in glue.rs). In fact, we don't really need Context to get the computed
// value of TimingFunction.
impl TimingFunction {
    /// Generate the ComputedTimingFunction without Context.
    pub fn to_computed_value_without_context(&self) -> ComputedTimingFunction {
        match &self {
            GenericTimingFunction::Steps(steps, pos) => {
                // Resolvable value was enforced at parse time
                GenericTimingFunction::Steps(steps.resolve().unwrap(), *pos)
            },
            GenericTimingFunction::CubicBezier { x1, y1, x2, y2 } => {
                // Resolvable value was enforced at parse time
                GenericTimingFunction::CubicBezier {
                    x1: x1.resolve().unwrap(),
                    y1: y1.resolve().unwrap(),
                    x2: x2.resolve().unwrap(),
                    y2: y2.resolve().unwrap(),
                }
            },
            GenericTimingFunction::Keyword(keyword) => GenericTimingFunction::Keyword(*keyword),
            GenericTimingFunction::LinearFunction(function) => {
                // Resolvable value was enforced at parse time
                GenericTimingFunction::LinearFunction(function.clone())
            },
        }
    }
}

impl ToComputedValue for TimingFunction {
    type ComputedValue = ComputedTimingFunction;
    fn to_computed_value(&self, _: &Context) -> Self::ComputedValue {
        self.to_computed_value_without_context()
    }

    fn from_computed_value(computed: &Self::ComputedValue) -> Self {
        match &computed {
            ComputedTimingFunction::Steps(steps, pos) => Self::Steps(Integer::new(*steps), *pos),
            ComputedTimingFunction::CubicBezier { x1, y1, x2, y2 } => Self::CubicBezier {
                x1: Number::new(*x1),
                y1: Number::new(*y1),
                x2: Number::new(*x2),
                y2: Number::new(*y2),
            },
            ComputedTimingFunction::Keyword(keyword) => GenericTimingFunction::Keyword(*keyword),
            ComputedTimingFunction::LinearFunction(function) => {
                GenericTimingFunction::LinearFunction(function.clone())
            },
        }
    }
}