Add eachregion(::AnnotatedString) implementation to Base

base/strings/annotated.jl

@@ -459,3 +459,113 @@ function annotated_chartransform(f::Function, str::AnnotatedString, state=nothin
     end
     AnnotatedString(String(take!(outstr)), annots)
 end
+
+struct RegionIterator{S <: AbstractString}
+    str::S
+    regions::Vector{UnitRange{Int}}
+    annotations::Vector{Vector{NamedTuple{(:label,:value),Tuple{Symbol,Any}}}}
+end
+
+length(si::RegionIterator) = length(si.regions)
+
+@propagate_inbounds function iterate(si::RegionIterator, i::Integer=1)
+    if i <= length(si.regions)
+        @inbounds ((SubString(si.str, si.regions[i]), si.annotations[i]), i+1)
+    end
+end
+
+eltype(::RegionIterator{S}) where { S <: AbstractString} =
+    Tuple{SubString{S}, Vector{NamedTuple{(:label,:value),Tuple{Symbol,Any}}}}
+
+"""
+    eachregion(s::AnnotatedString{S})
+    eachregion(s::SubString{AnnotatedString{S}})
+
+Identify the contiguous substrings of `s` with a constant annotations, and return
+an iterator which provides each substring and the applicable annotations as a
+`Tuple{SubString{S}, Vector{NamedTuple{(:label,:value),Tuple{Symbol,Any}}}}`.
+
+# Examples
+
+```jldoctest
+julia> collect(eachregion(AnnotatedString(
+           "hey there", [(1:3, :face, :bold), (5:9, :face, :italic)])))
+3-element Vector{Tuple{SubString{String}, Vector{@NamedTuple{label::Symbol, value}}}}:
+ ("hey", [@NamedTuple{label::Symbol, value}((:face, :bold))])
+ (" ", [])
+ ("there", [@NamedTuple{label::Symbol, value}((:face, :italic))])
+```
+"""
+function eachregion(s::AnnotatedString, subregion::UnitRange{Int}=firstindex(s):lastindex(s))
+    isempty(s) || isempty(subregion) &&
+        return RegionIterator(s.string, UnitRange{Int}[], Vector{NamedTuple{(:label,:value),Tuple{Symbol,Any}}}[])
+    events = annotation_events(s, subregion)
+    isempty(events) && return RegionIterator(s.string, [subregion], [NamedTuple{(:label,:value),Tuple{Symbol,Any}}[]])
+    annotvals = NamedTuple{(:label,:value),Tuple{Symbol,Any}}[
+        (; label, value) for (; label, value) in annotations(s)]
+    regions = Vector{UnitRange{Int}}()
+    annots = Vector{Vector{NamedTuple{(:label,:value),Tuple{Symbol,Any}}}}()
+    pos = first(events).pos
+    if pos > first(subregion)
+        push!(regions, thisind(s, first(subregion)):prevind(s, pos))
+        push!(annots, [])
+    end
+    activelist = Int[]
+    for event in events
+        if event.pos != pos
+            push!(regions, pos:prevind(s, event.pos))
+            push!(annots, annotvals[activelist])
+            pos = event.pos
+        end
+        if event.active
+            insert!(activelist, searchsortedfirst(activelist, event.index), event.index)
+        else
+            deleteat!(activelist, searchsortedfirst(activelist, event.index))
+        end
+    end
+    if last(events).pos < nextind(s, last(subregion))
+        push!(regions, last(events).pos:thisind(s, last(subregion)))
+        push!(annots, [])
+    end
+    RegionIterator(s.string, regions, annots)
+end
+
+function eachregion(s::SubString{<:AnnotatedString}, pos::UnitRange{Int}=firstindex(s):lastindex(s))
+    if isempty(s)
+        RegionIterator(
+            s.string,
+            Vector{UnitRange{Int}}(),
+            Vector{Vector{NamedTuple{(:label,:value),Tuple{Symbol,Any}}}}(),
+        )
+    else
+        eachregion(s.string, first(pos)+s.offset:last(pos)+s.offset)
+    end
+end
+
+"""
+annotation_events(string::AbstractString, annots::Vector{@NamedTuple{region::UnitRange{Int},label::Symbol,value::Any}}, subregion::UnitRange{Int})
+    annotation_events(string::AnnotatedString, subregion::UnitRange{Int})
+
+Find all annotation "change events" that occur within a `subregion` of `annots`,
+with respect to `string`. When `string` is styled, `annots` is inferred.
+
+Each change event is given in the form of a `@NamedTuple{pos::Int, active::Bool,
+index::Int}` where `pos` is the position of the event, `active` is a boolean
+indicating whether the annotation is being activated or deactivated, and `index`
+is the index of the annotation in question.
+"""
+function annotation_events(s::AbstractString, annots::Vector{NamedTuple{(:region,:label,:value),Tuple{UnitRange{Int},Symbol,Any}}}, subregion::UnitRange{Int})
+    events = Vector{NamedTuple{(:pos, :active, :index), Tuple{Int, Bool, Int}}}() # Position, Active?, Annotation index
+    for (i, (; region)) in enumerate(annots)
+        if !isempty(intersect(subregion, region))
+            start, stop = max(first(subregion), first(region)), min(last(subregion), last(region))
+            start <= stop || continue # Currently can't handle empty regions
+            push!(events, (pos=thisind(s, start), active=true, index=i))
+            push!(events, (pos=nextind(s, stop), active=false, index=i))
+        end
+    end
+    sort(events, by=e -> e.pos)
+end
+
+annotation_events(s::AnnotatedString, subregion::UnitRange{Int}) =
+    annotation_events(s.string, annotations(s), subregion)